Bonding in Solids Valentin Panyushenko Chris Zheng

Molecular Solids  Held together by intermolecular forces  Forces are weak; solid soft; low melting points  Typically gas or liquid in room temperature  Ex. Ar, H 2 O, CO 2

Molecular Solids  Property of molecular solids depend on: Strength of the forces Strength of the forces Abilities of molecules to pack efficiently in 3D Abilities of molecules to pack efficiently in 3D CH 3 OH Benzene Toluene Phenol Melting point (˚C) Boiling point (˚C)

Intermolecular Forces  London dispersion: weakest; result from attractions between dipoles  H Bonding: strongest; molecules containing H bond to an electro- negative element  Dipole-dipole: attraction between the + end of one molecule and the – end of another

Covalent-Network Solids  Held together by covalent bonds  Compared to molecular solids: harder and higher melting points  In diamond: Each C is bonded to four other C Each C is bonded to four other C Melting point: 3550 ˚C Diamond

Covalent-Network Solids  Graphite: C atoms arranged in hexagonal ring C atoms arranged in hexagonal ring Each C is bonded to three others in the layer Each C is bonded to three others in the layer Good conductor of electricity b/c delocalized π bonds Good conductor of electricity b/c delocalized π bonds Used as lubricant and the “lead” in pencils Used as lubricant and the “lead” in pencils Graphite Melting point: 3652 – 3697 ˚C

Ionic Solids  Ions held together by ionic bonds  Strength of ionic bonds depend on the charges  Structure depend on charges and sizes of ions  NaCl: each Na + ion is surrounded by 6 Cl - ions Gray: Na. Green: Cl

Ionic Solid Structures  ZnS: Zn 2+ ions surround tetrahedrally by four S 2- ions Blue: S. Yellow: Zn  CaF 2 : There are twice as many F - ions as Ca 2+ ions  CsCl: each Cs + ion is surrounded by eight Cl - ions Gray: Ca. Green: F Gray: Cs. Green: Cl

Metallic Solids  Consist entirely of metal atoms  Each atom has 8 or 12 adjacent atoms  Bonding due to delocalized valence e -  Strength of bonding ↑ as # of valence e - ↑  Good conductors b/c of the mobility of e -

 Body Center-Cubic (BCC): atoms on each corner  Atoms: Li, Na, K, Cr, Ba, etc.  Hexagonal Close-Packed (HCP): 3 layers – top and bottom with 7 e-, and middle with 3 e-  Atoms: Mg, Zn, Ti, Be, etc. Metallic Bond Structures  Face-Center-Cubic (FCC): atoms on each corner & center of each face  Atoms: Al, Au, Ag, Ni, Pt, etc.

Additional Sources  act/c123/intermol.html act/c123/intermol.html act/c123/intermol.html  crystal_structure_visualization.htm crystal_structure_visualization.htm crystal_structure_visualization.htm  scussion6.html scussion6.html scussion6.html  ed.org/EducationResources/CommunityCo llege/Materials/Structure/metallic_structure s.htm ed.org/EducationResources/CommunityCo llege/Materials/Structure/metallic_structure s.htm ed.org/EducationResources/CommunityCo llege/Materials/Structure/metallic_structure s.htm